Container for liquefied gases

ABSTRACT

1,186,060. Carrying liquefied gases. CONCH OCEAN Ltd. 9 Oct., 1968 [31 Oct., 1967], No. 49426/67. Headings B7A and B7S. [Also in Division F4] Heat insulation material 16, 17, 20, 21, Fig. 3, surrounding a cold liquidized gas storage tank 15 of polygonal form, Fig. 2, has embedded therein near the outer surface a film of water impermeable material 19 extending parallel to the tank sides whereby any water or water vapour which penetrates the outer thickness 20 of the insulation which is permeable runs down the film 19 and is collected in a recess 13a in an outer tank 13, e.g. the inner hull of a tanker. The insulation comprises a thick layer 17 of balsa wood mounted on spaced water impermeable wood strips 16 attached to the inner hull 13, a layer of permeable fibreglass 20 between adjacent strips 16 and impermeable fibreglass 21 between layer 17 and the film 19. The latter may be of metal or plastics material and is adhesively secured to the strips 16, which are provided with drain holes 16a. In a modification the storage tank is of the self-supporting type and the insulation which is spaced therefrom comprises a thick inner layer of balsa wood and a thin outer layer of fibreglass between which layers the water impermeable film is sandwiched; provision being made for collecting water running down the outer surface of the film and also for collecting leakage from the tank as described in Specification 919,755.

I Umted States Patent 1 13,537,415

[72] Inventor Robert G. Jackson [56] References Cited llornshurchimxi England UNITED STATES PATENTS I211 P 22 968 3,136,135 6/1964 Rigby et al 1l4/74(A)UX 523 3 1970 3,422,719 1/1969 Becker l14/74(A)UX A UX Assign Conch ocean Limited 3, 98,205 2/1969 Basile et al 114/74( Nassau,The Bahamas, Great Britain P mary xammer Trygve M. Bhx a company of the Bahamas y- Max Llbman [32] Priority Oct. 31, 1967 H3 ital fgz n ABSTRACT: The present invention relates to a container of the kind for containing very cold liquids and comprising a tank (l, 15) of cold resistant material surrounded by thermal insulation (2, 14) characterized by the provision of a thin substan- [54] ZE? IgiQUEFIED GASES tially water-impermeable film or foil extending parallel, or 8 claims raw 8 generally so, to the exterior surfaces of the sidewalls and, op- [52] U.S. Cl 114/74, tionally, the bottom of the tank and located within the 220/15 thickness of the surrounding thermal insulation adjacent the [51] Int. Cl. B63b 25/16, external face thereof, i.e. the face remote from the tank, such 865d 25/00 that any water or water vapour which penetrates the outer [50] Field of Search 114/74, thickness of insulation runs down the film or foil and is col- 74A; 220/15 lected adjacent the bottom ofthe tank.

Patented Nov. 3,1970 I 3,537,415

Sheet 1 of 3 I nvenlor Roberf GJa cks on By MMf/M A Home y Patented Nov. 3', 1970 Sheet IlIllIlvTtliIlIl-l ////K/ L ///A Inventor Robe H G \L c/rson Attorney Patented Nov. 3, 1970 Sheet I Roberf 6. Jackso Attorney CONTAINER FOR LIQUEFIED GASES BACKGROUND OF THE INVENTION This invention relates to containers used for the storage and transport of very cold liquids and of the kind comprising a tank of cold resistant material surrounded by thermal insulation. The invention is primarily intended for containers of the kind defined above for liquefied gases at near-atmospheric pressure and low temperature.

Containers of the kind defined above are of two distinct types. In one type, the container comprises a self-supporting tank, that is to say one having sufficient structural strength to hold the liquid within the tank and withstand the hydrostatic pressures and any inertia forces, without depending upon any other means outside the tank for aid in supporting the walls of the tank against buckling. The tank is of a material, e.g.metal, which is cold resistant, Le. which is not subject to cold embrittlement at the temperature met in use, for example, the temperature of liquefied gas. The tank is enclosed by an external housing of thermal insulation, which either directly encases the tank or lines an outer shell, so as to define a containing space within which the tank is located, with or without a gap between its exterior surface and the interior surface of the insulation.

The other type of container is know as an integrated container and comprises a housing of solid load-bearing thermal insulation lined with a thin and flexible fluid-tight membrane tank of sheet material, e.g. metal, which is not subject to cold embrittlement at the temperature which will be encountered in use and which is not self-supporting, but is supported, against internal loads due to hydrostatic pressures of contained fluid and any inertia forces, by the surrounding solid insulation. The insulation lines and is itself supported by, a substantially rigid supporting shellso that the insulation directly transmits to the supporting shell all the pressure exerted by the contained fluid upon the walls of the membrane tank.

Containers of both of these types are intended to be used, either for storage on land or for transport, for example, in tanker ships for the overwater transportation of very cold liquids such as liquefied gases. Such tanker ships usually have a double hull and the inner hull is divided by transverse bulkheads so as to divide the hull into individual cargo holds in which the containers of either type are located. .The space between the hulls, and possibly also the spaces between adjoining transverse bulkheads, is or are divided into tanks to contain water. Such water is provided for two purposes. One purpose is to serve as ballast for trimming and safe operation of the tanker ship. In this regard, it is to be noted that in the case of a tanker ship for transporting liquefied gases, which are of low density, at least some ballast water may be provided in at least some of the ballast tanks even when the cargo tanks are full of liquid cargo. The second purpose is that, should there be a failure of a cargo tank or of the insulation thereof, the ballast tank adjacent the affected part of the insulation can be filled with water thus preventing the steel of the inner hull from being cooled below the safe level.

A problem encountered in the use of containers of the kind concerned in tanker ships is that, should aleak develop in a wall of a ballast tank at the side adjacent the cargo tank, then water will penetrate into the insulation which will usually be partially water permeable, and will tend to flow towards the tank. There is, of course, a thermal gradient across the thickness of the insulation when the tank contains cold cargo and water penetrating the insulation towards the tank will progressively become colder and when it arrives at a location below the freezing point of water it will freeze. Accordingly, ice will build up within the outer thickness of the insulation. A serious difficulty then arises in that ice has a greater coefficient of thermal conduction than the thermal insulation so that the thermal insulating properties of the insulation are A similar problem arises in the case of a land storage container comprising a tank enclosed in a layer of thermal insulation. Although it is usual for the insulation to be enclosed in an outer shell the latter may develop faults so that it is not sealed from the atmosphere. Atmospheric moisture may then enter the outer shell and penetrate the insulation and will freeze. As the ice builds up it will reduce the effectiveness of the thermal insulation.

The aim of the present invention is to overcome these problems and provide, for very cold liquids, a container of the kind defined and of either type specified above, in which the formation of ice within the thermal insulation is prevented or considerably reduced.

In accordance with the'present invention there is provided, within the thermal insulation of a container of the kind defined, a thin substantially water-impermeable film or foil extending parallel or generally so, to the exterior surface of the sidewalls of the tank and located within the thickness of the insulation adjacent but spaced a short distance inwardly from the external face thereof, i.e. the face remote from the tank.

The idea of the present invention is that the substantially water-impermeable film will prevent any significant quantity of water or water vapour, which has penetrated the outer thickness of the insulation, from further penetrating the insulation. By reason of its location near to the outer face of the insulation, the film or foil will be at a temperature above the freezing point of water so that the water will not freeze but will run down the outer face of the film through the outer thickness of the insulation and collect adjacent the bottom of the tank. Thus, the film or foil will be located at such a position within the thickness of the insulation that under normal conditions with the container loaded with a very cold liquid the film or foil will .be at a temperature a little above the freezing point of water.

The film or foil may be of any of various materials. Thus, it may be a film of a suitable plastics material. As examples may be mentioned polyethylene, polypropylene, polyvinylchloride and nylon andthe plastics films marketed under the registered trade marks Mylar, Neoprene, Teflon" and Melinex". The film or foil could also be constituted by a metal foil, such for example'as aluminum, copper or stainless steel, although where the container is to be used in a tanker ship the foil would probably require to be coated, on at least that face which will be contacted by sea water (since the water used in ballast tanks is usually sea water), with a material protecting the foil from corrosion by any impurities in the sea water. The film or foil could, in fact, be constituted by a laminate of a metal foil and a plastics film, or by a plastics film provided on one face with a metalised foil. Examples of the latter are aluminized Mylar" and copper polyester. Moreover, the film or foil could be constituted by a woven fabric of either natural fibre such as rayon, or manmade fibre such as Terylene which is plasticized, rubberized or otherwise treated to render it substantially water impermeable. The film or foil might even be constituted by one of the commercially available waterproof papers. These are examples only of many materials which could be employed as, and which meet the requirements of, the film for foil.

These requirements are that the film or foil must have adequate tensile strength, tear resistance and be substantially impermeable to'water, i.e.have an extremely low permeability to water. The degree of water impermeability which is required and which is meant by the phrase substantially water impermeable may vary depending upon the use and location of the container but should in most applications preferably have a permeability of less than 10- kg./m.2/sec. The film or foil must be of a thickness to provide the requisite tensile strength, tear resistance and be substantially water impermeable. This will vary depending-upon the material of the film or foil and the environment of use of the container but it is thought that the film or foil should not be less than onethousandth of an inch or 0.025 of a millimetre in thickness and preferably should be of the order of five-thousandths of an inch or 0.125 of a millimetre in thickness.

Preferably the arrangement is such that the water is collected adjacent the bottom of the tank; that is to say, a water impermeable receptacle may be provided below the bottom of the tank. This receptacle may be in the form of a tray into which the lower ends of the film or foil associated with the sidewalls of the tank extend. This receptacle could be constituted by a portion of film or foil but is preferably of somewhat thicker material. Thus, water running down the outer faces of the film or foil adjacent the sidewalls of the tank will be collected in the receptacle from where it can be removed. Preferably a pump or equivalent means is provided for removing the water which collects in the receptacle. Where the container is located in the cargo hold of a tanker ship the bottom of the cargo hold may constitute the watercnllectlng tray or may he formed or provided with a receptacle or sump. The water collecting in the cargo hold is preferably removed, either by being allowed to flow through a hole connecting the sump with the space between the inner and outer hulls perhaps controlled by a nonreturn valve, or through pipes and an associated pump located within the space between the inner and outer hulls.

In any event, a water impervious barrier will preferably also be provided for preventing water from travelling up through the insulation below the bottom of the tank under the action of the pressure head of water. This barrier will advantageously be constituted by film or foil arranged in the same relation to the bottom of the tank as the film or foil is arranged in relation to the sidewalls of the tank, that is, substantially parallel to the bottom adjacent the lower or outer face of the insulation and preventing any water which has penetrated the lower or outer thickness of the bottom insulation from further penetrating the bottom insulation.

Manifestly, at least the outer thickness of the thermal insulation exterior of the film or foil must be very permeable to water to enable the water to penetrate this thickness of the insulation and to enable the water to run down the outer face of the film or foil. Suitable water-permeable thermal insulations are glass fiber, wool, mineral wool or rock wool.

The thermal insulation can be of one material or one combination of materials only, that is to say the portions at both sides of the film or foil can be of identical material or combination of materials. Alternatively, the insulation at opposite sides of the film or foil may be of different materials or combinations. In any event, in view of the considerable thermal gradient through the thickness of the thermal insulation in use and the necessity to locate the film or foil at a relatively .warm location so that it will normally be at a temperature above the freezing point of water adjacent the exterior surface of the insulation, the inner layer of insulation between the tank and the film or foil may be relatively thick, whereas the outer layer of thermal insulation, exterior of the film or foil may be relatively thin.

The film or foil may be in the form of a continuous membrane forming a continuous substantially water-impermeable wall surrounding at least the sidewalls ofthe tank. Alternatively, the film or foil may be in sections which are sealingly engaged with other substantially water-impermeable parts so that the whole constitutes a water-impermeable barrier. In this respect it is known to mount thermal insulation for a container of the kind concerned and in the form of blocks or pads, for example within the hold of a ship, by securing the pads to spaced securing strips of water-impermeable material which are secured to the inner hull. In this case thermal insulation could be provided between the adjacent strips and incorporate a thin section of film or foil dimensioned to fill the space between the strips and sealingly secured to the strips so that all the sections together will the strips form a continuous waterimpermeable barrier. In this arrangement, the horizontal strips are preferably formed with vertical slots or apertures enabling water running down the film or foil to pass therethrough and into the collecting receptacle adjacent the bottom of the tank.

In order that the invention may be more clearly understood two specific constructional examples will now be described with reference to the accompanying drawings, wherein:

FIG. I is a vertical crosssectional view through a container comprising a free-standing tank;

FIG. 2 is a vertical cross-sectional view through a marine tanker incorporating a container comprising a membrane tank; and

FIG. 3 is a detailed sectional view through one of the fixing strips of FIG. 2.

It will be understoodthat the drawings are not to scale.

In FIG. 1 the self-supporting polygonal tank is indicated generally at 1. This is of metal which is not subject to cold em brittlement and of a sufficient thickness to contain the liquid. The tank is surrounded by thermal insulation, generally designated 2, which is itself enclosed in an outer shell 3. There is a space "S" all around the tank between the exterior surface of the tank and the Internal surface of the insulation 2. The illustrated tank is in fact, that described and claimed in the complete specification of US. Pat. No. 3,110,157 in which a receptacle 4 is provided between the bottom of the tank and the internal or upper surface of the bottom of the insulation. This receptacle is in the form of a tray having a continuous upwardly directed wall 4a extending for a limited distance up wardly adjacent the lower portions of the sidewalls of the tank. This receptacle is of a material which is not subject to cold embrittlement and is intended to collect any of the very cold fluid cargo escaping from the tank as a result of a minor leak in the latter. This escaping fluid will be collected in the receptacle and will be removed therefrom through pipes 5 by means of a pump 6.

In accordance with the present invention there is incorporated in the sidewalls and bottom of the thermal insulation, Le. the walls enclosing the sidewalls of the tank and, the insulation below the bottom of the tank, a continuous thin film or foil 7 which constitutes a substantially water-impermeable barrier. Thus, in this example the film or foil constitutes a membrane extending substantially continuously around and parallel to both the sidewalls and the bottom of the tank.

Thus the thermal insulation 2 comprises a relatively thick inner layer 8 of a suitable thermal insulation which is substantially fluid impermeable, e.g. balsa wood faced with plywood, or a suitable plastics material, and a relatively thin layer 9 of a thermal insulating material which is water permeable e.g. fiber glass. The film or foil is interposed between the layers 8 and 9. The opposed faces of the film or foil are preferably secured to the contacting faces of the opposed layers 8 and 9 by a suitable adhesive.

In this example the bottom of the outer shell 3 is itself employed as a water receptacle. Accordingly the bottom of the shell 3 is formed either with an annular channel extending around the bottom adjacent the side walls or with one or more small sumps for the collection of water. The water can be removed through pipes 10 by means of a pump 11. Alternatively, the channel or sumps 3a could simply be formed with a drain hole, for example, controlled by a nonreturn valve.

It will be appreciated that the bottom of the tank will be supported against static loads by conventional means not fully shown in the drawings. The container of FIG. 1 could be applied to a tanker ship in the same manner as is the container to be described with reference to FIG. 2. In this event, the outer shell 3 could be constituted by the walls of the cargo hold of the tanker ship.

In FIG. 2 there is shown a marine tanker having an outer hull l2 and an inner hull l3. Disposed within a cargo hold defined within the inner hull is a container comprising thermal insulation, indicated generally at 14 internally lining the cargo hold and of load-bearing material. Disposed within the thermal insulation and in contact with the inner surface thereof is a polygonal membrane tank 15 of thin material not subject to cold embrittlement.

The thermal insulation comprises a plurality of substantially I water impermeable timber ground strips 16 attached at regular intervals to the walls and bottom of the cargo hold and some of which (as shown) extend horizontally and someof which extend vertically (not shown). The ground strips also extend longitudinally, along the bottom (as shown) and transversely (not shown). Mounted upon the strips is a relatively thick layer 17 of the thermal insulation which may for example comprise blocks of balsa wood, faced with plywood, for example as disclosed in U.S. Pat. No.3,l12,043 constituting a secondary barrier against leakage of very cold liquid cargo.

A water impermeable thermal insulation, indicated generally at 18, is provided between the adjacent strips 16 on the sidewalls and bottom of the cargo hold and incorporates a thin section of film or foil 19 filling the space between the strips 16 and sealingly secured to the strips e.g. by adhesive tape, so that all the sections of film or foil, with the strips 16 form a continuous water-impermeable barrier extending adjacent and parallel to the sidewalls and the bottom of the tank. The insulation 18 comprises one layer of fibre glass 20 between the film or foil 19 and the shell 13 and another layer of fibre glass 21 between the film or foil 19 and the insulation 17.

In this example, the bottom of the inner hull 13 is itself employed as a water receptacle. Accordingly, the bottom of the inner hull is formed with formation 13a which may be either liquid, the film or foil is at a temperature above the freezing point of water;

e. an outer normally fluid-tight supporting shell surrounding said film of fluid-impervious material; and

f. sump means at the bottom of the tank for collecting by gravity any fluid which penetrates from the exterior of the container through said outer shell before it can build up substantial hydrostatic pressure against said thin film, so as to prevent such leakage fluid from coming into contact with said layer of thermal insulation.

2. The invention according to claim 1, said sump means being in the form of an annular trough at the bottom of the tank.

3. The invention according to claim 2, and means for withdrawing fluid from said sump means.

4. A container according to claim 3, wherein the film or foil is in sections which are sealingly engaged with other fluid-iman annular channel extending around the bottom adjacent the sidewalls or small spaced sumps, e.g. four in each cargo hold near bottom corners of tank, for the collection of water. The water can be removed through pipes 22 by a pump 23 located between the inner and outer hulls. Alternatively, instead of the pump and pipes the sumps may simply be connected with the bottom space between the inner and outer hulls of the tanker ship by drain holes, for example controlled by nonreturn valves.

There may be gaps between the strips 16 and the walls of the cargo hold which may be adequate for the drainage of water therethrough. Preferably, however, the horizontal strips 16 adjacent the sidewalls and the longitudinal strips 16 below the bottom of the tank are formed with slots or apertures 16a as shown in FIG. 3 permitting the water to pass through the strips.

d. said layer of thermal insulation being such that under normal conditions, with the container loaded with very cold permeable parts 16 so that the whole constitutes a substantially water-impermeablebarrier.

5. A container according to claim 4, wherein the outer supporting shell 3, 13 is rigid and wherein the thermal insulation includes blocks or pads 17 secured to spaced securing strips 16 I of substantially water-impermeable material which are secured to and space the blocks or pads from the outer shell and thermal insu ation of permeable material 20, 21, e.g. glass fibre, provided between the adjacent strips 16.

6. A container according to claim 4, wherein the thermal insulation between the strips incorporates within its thickness and near to the outer face thin sections of film or foil, dimensioned to fill the spaces between adjacent strips and sealingly secured to the strips so that all the sections of film or foil together with the strips, form a continuous substantially waterimpermeable barrier.

7. A container according to claim 6, wherein the spaced strips are formed with vertical slots or apertures enabling water running down the film or foil to pass therethrough and into the receptacle adjacent the bottom of the tank.

I 8. A container for very cold liquids, said container compris ing:

a tank of cold resistant material;

a relatively thick main layer of thermal insulation surrounding said tank;

a very thin nonload-bearing waterproof film adjacent the exterior surface of said main thermal insulation;

a relatively thin layer of water-permeable thermal insulation surrounding and adjacent to said thin waterproof film along at least the sidewalls of a tank; and

receptacle means exterior to and at the bottom of the tank for collecting water from said layer of water-permeable thermal insulation. 

